Modeling of the separation performance of nanofiltration membranes and its role in the applications of nanofiltration technology in product separation processes

Abstract

Although there is a voluminous literature on the determination of structural parameters (the pore radius, the ratio of membrane porosity to membrane thickness) of a nanofiltration (NF) membrane and its separation performance (such as the rejection and the permeation flux) by the simplified Teorell-Meyer-Sievers (TMS) model, little of this research comments on other theories and the consequences of linking modeling evaluation to technological application. Theories used to predict the separation performance of an NF membrane usually include: the non-equilibrium thermodynamic model, the pore model, the space charge model, the TMS model, the electrostatic and steric-hindrance model, and the semiempirical model. In the article, we briefly trace the origins or the general ideas of the above-mentioned theories. From there, recent researches on the characterization of membrane structural parameters and electrical properties (such as the surface charge density q_w) are reviewed. We then turn to research on the separation performance of an NF membrane for single-component solutions of inorganic electrolytes, neutral organic solutions, and a mixture solution of electrolytes or that of an electrolyte and neutral organic solute. Afterwards, we outline the applications of NF technology in the processes of product separation and conclude with a discussion on the role of models in such applications.